Knowledge of cooperative breeding in birds from longitudinal studies is available only for a small proportion of species. This paper reports data from a 12‐year study on the Tibetan Ground Tit Pseudopodoces humilis. On average, 27.2% (range: 13.0–36.1%) of monogamous pairs in each year contained one (85.4%) or more (14.6%) male helpers, 83.7% of which were yearlings staying on natal territories. Most helpers (89.6%) helped once and then bred independently. Adults had male‐biased sex ratios, low annual survival rates (averaging 0.50) and shorter longevities (averaging 1.8 years) compared with low‐altitude avian cooperative breeders, suggesting that mate shortage promotes helping behaviour in this species. Incest occurred rarely (2.1% of pairs), probably because kin recognition occurs through year‐around living in family groups. There was a low level (3.1% of broods) of extra‐pair parentage, which could facilitate the maintenance of cooperative breeding.
How can altruism evolve or be maintained in a selfish world? Hamilton's rule shows that the former process will occur when > -the benefits to the recipients of an altruistic act, weighted by the relatedness between the social partners , exceed the costs to the altruists-drives altruistic genotypes spreading against nonaltruistic ones. From this rule, we infer that altruistic genotypes will persist in a population by forming a stable heritable polymorphism with nonaltruistic genotypes if = makes inclusive fitness of the two morphs equal. We test this prediction using the data of 12 years of study on a cooperatively breeding bird, the Tibetan ground tit , where helping is performed by males only and kin-directed. Individual variation in ever acting as a helper was heritable ( = 0.47), and the resultant altruism polymorphism remained stable as indicated by low-level annual fluctuation of the percentage of helpers among all adult males (24-28%). Helpers' indirect fitness gains from increased lifetime reproductive success of related breeders statistically fully compensated for their lifetime direct fitness losses, suggesting that = holds. While our work provides a fundamental support for Hamilton's idea, it highlights the equivalent inclusive fitness returns to altruists and nonaltruists mediated by = as a theoretically and realistically important mechanism to maintain social polymorphism.
While knowledge on birds’ breeding ecology is essential for understanding avian adaptation and managing conservation, it is poorly studied for many species, even for some common species. The knowledge of the natural history of the red-billed blue magpie (Urocissa erythrorhyncha), a species widely distributed in China and Southeast Asia, is sketchy. Here we present detailed data of nest site selection and the breeding ecology of red-billed blue magpie in central China, and of the effects of nest predation and brood parasitism on reproductive strategies. Most nests were built on Phyllostachys sulphurea and Quercus acutissima. Breeding season ranged from March to August. The first egg was laid between early April and late July. The incubation period lasted 15 days and the nestling period, 18 days. Average clutch size was 4.6 eggs, and brood size at fledging was 3.3 young. Overall, 43.8% of nesting attempts successfully produced at least one fledged young. Nest predation and brood parasitism were the two main reasons for fledging failure, which mainly occurred after April. Correspondingly, U. erythrorhyncha showed a tendency to build nests higher up and have a smaller clutch size in late stages of the breeding season. This study provides the first reliable and comprehensive information on the reproductive parameters of U. erythrorhyncha, which will lay a foundation for further understanding this species’ biology and opens up an avenue for large-scale comparative studies of the Urocissa genus or higher-level taxa.
OM (2017) Association theory: A new framework for analyzing social evolution. bioRxiv:197632. 4 Hamilton WD (1964) The genetical evolution of social behaviour. I. J Theor Biol 7:1-16. 5 Dawkins R (1979) Twelve misunderstandings of kin selection. Ethology 51:184-200.
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